Have you tried to nest the formula with an if statement? Where you would say
=if(a1=b1,1,if(isblank(b1),0,day(b1-a1)))

"mac56er" wrote:

I need to calculate the total number of days for a project. The spreadsheet
is set up to calculate the number of days for each month and then sum the
total of days. However, I cannot figure out the formula to calculate when
the beginning and end date is the same. For example, the projects ends on 1
Jun 08. The total number of days for June needs to be 1. Also, if a month
has no dates, the result should be 0. Any suggestions?